It is known to add talc as a reinforcing substance to polycarbonate compositions in order to increase the rigidity and tensile strength, to increase the dimensional stability during variations in temperature and to improve the surface properties. The talc added also serves as a flameproofing synergist in flame-resistant materials.
WO 98/51737 A1 discloses PC/SAN blends which have polystyrene-grafted polybutadiene rubber as an impact modifier and comprise mineral fillers, e.g. talc, with an average particle size of preferably 1.5 to 5 μm. The molding compositions described are not given a flame-resistant treatment. It furthermore emerges from the examples that molding compositions which comprise talc with a particle size of <1.5 mm have a low melt volume index (MVI). The PC/SAN blends described with polystyrene-grafted polybutadiene rubber show deficits in the mechanical properties.
U.S. Pat. No. 5,162,410 describes PC/ABS molding compositions which comprise talc with an average particle size of 1.5 to 20 μm, preferably 4.0 to 10 μm, to improve the surface appearance of injection-molded finished components. The molding compositions described are distinguished by a matt surface and improved mechanical properties.
JP-A 11/199768 discloses flame-resistant PC/ABS compositions comprising talc and phosphoric acid esters, 90 wt. % of the talc having a particle size of <4 μm. The PC/ABS compositions described have improved burning properties and are suitable in particular for thin wall applications. Molding compositions with talc types with average particle diameters in the sub-micro range are not described, nor are there indications that an improvement in the mechanical properties, in particular the elongation at break and bonding strength can be improved by using such types.
U.S. Pat. No. 5,091,461 discloses PC/ABS compositions which comprise as the reinforcing substance talc and non-calcined clay minerals. The talc types used have a particle size of less than 44 μm (=44,000 nm). The PC/ABS compositions are distinguished by a reduced linear thermal expansion coefficient and a relatively high impact strength at low temperatures.
EP-A 0 758 003 A2 describes PC molding compositions which can comprise inorganic fillers with a particle diameter of >0.5 mm as the reinforcing substance. Talc with a particle diameter of ≧0.2 mm is mentioned, inter alia, as a filler. The PC molding compositions can furthermore be given a flame-resistant treatment and are distinguished by an improved surface appearance and a high modulus of elasticity. Polycarbonate blends are not described in this specification.
A disadvantage of the talc-containing PC/ABS blends known from the prior art is that an increase in the E modulus is indeed achieved by the addition of talc, but at the same time other mechanical properties, such as elongation at break and toughness, are impaired. The addition of talc to PC/ABS blends as a rule leads to a significant deterioration in the toughness of the shaped article produced from the composition. Either the toughness achieved by addition of talc is often therefore not sufficient for specific uses, or the amount of the inorganic material employed is too low to realize the property advantages intended from its addition to a sufficient extent.
In addition, the weld line strength in known talc-containing PC/ABS blends is often inadequate.
It is thus desirable to provide polycarbonate compositions to which talc is added in a known manner for the purpose of improving at least one material property, but which are distinguished by an improved level of toughness and/or toughness at low temperatures compared with the prior art and an increased weld line strength. In particular, the polycarbonate compositions should be distinguished by an improved toughness at low temperatures with simultaneously good values for the elongation at break and E modulus.
The polycarbonate composition according to the invention should exhibit a good processing behavior, i.e. high melt flow rate.